Display device

ABSTRACT

A display device utilizing discharges in a gas wherein a subsidiary discharge is employed to facilitate the occurrence of main discharges which are adapted to be used for displaying characters, numerals, figures, patterns or the like, characterized in that said subsidiary discharges are produced by pulse voltages and at the same time therewith display signals representing said characters, numerals, figures, patterns or the like are supplied for producing the main discharges.

United States Patent; 11 1 Kaji et a1.

1111 3,895,371 451 July 15,1975

1 1 DISPLAY DEVICE [75] lnventors: Tetsunori Kaji; Seiichi Murayama;

Masakazu Fukushima, all of Kokubunji, Japan [73] Assignee: Hitachi, Ltd.,'.lapan [22] Filed: Oct. 29, 1973 [21] Appl. No.: 410,568

[30] Foreign Application Priority Data Oct. 27, 1972 Japan 47-107197 52 us. (:1 340/324 M; 315/169 TV 511 Int. Cl. G08b 55/36 [58] Field 61" Search ..340/324 M; 315/169 R,

315/169 T, 169 TV [56] References Cited UNITED STATES PATENTS 2,702,357 2/1955 Townsend 315/169 T 3,526,711 9/1970 Boer 340/324 M 3,654,508 4/1972 Caras 315/169 TV 3,681,754 8/1972 Baasch 340/166 R 3,727,102 4/1973 Johnson 315/169 R 3,795,908 3/1974 McDowell et al 340/324 M Primary Examiner-David L. Trafton Attorney, Agent, or Firm-Craig & Antonelli 5 7 ABSTRACT A display device utilizing discharges in a gas wherein a subsidiary discharge is employed to facilitate the occu'rrence of main discharges which are adapted to be used-for displaying characters, numerals, figures, patterns or the like, characterized in that said subsidiary discharges are produced by pulse voltages and at the san'i'e time therewith display signals representing said characters, numerals, figures, patterns or the like are supplied for producing the main discharges.

7 Claims, 15 Drawing Figures PATENTEDJUL 15 m5- SHEET FIG. I PRIOR ART ART FIG. 2

SHEET PATENTEDJUL 15 ms FIG. 3

WAVE-FORM OF sQuRcE 6 WAVE: FORM OF souRcE 7 WAVE FORM OF SOURCES wAvgi' FORM OF SOURCE 9 WAVE FORM OF SOURCEIO SUBSIDIARY P-ESCHARGE CUERENT Isd FIG. 5

P" fNTEnJuL 15 I915 ZTR PULSE WAVE FORM Lam 0 SOURCE 6 L ilr ql PULSE A E FORM v4 0F SOURCE l0 isd PATEM JUL SMS' 3.895371 SHEET 5 FIG.

PULSE WAVE FQRM OF FFQHTR SQURCE 6 l FIG [3 DISPLAY DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device utilizing direct current or d.c. discharges in a gas, and more particularly to a display device employing a plurality of main discharges and a plurality of subsidiary discharges to facilitate the starting of said main discharges.

2. Description of the Prior Art One of hitherto known display devices has an arrangement of electrodes such as schematically shown in FIG. 1, in which reference numerals l-l, 1-2 and 1-3 indicate anodes for the main discharges, 2-1, 22 and 2-3 indicate cathodes common to the main and subsidiary discharges, while numerals 4-1, 4-2 and 4-3 represent anodes for the subsidiary discharges. The cathodes 2-1, 22 and 2-3 have, respectively, through-holes 3-1, 3-2 and 3-3. All of the anodes l for the main discharges, the cathodes 2 and the anodes 4 for the subsidiary discharges are disposed in the atmosphere of the same type of gas.

As is well known, the function of the subsidiary discharges is to facilitate the starting of the main discharges. When the subsidiary discharges occur, electrons or metastable atoms reach the main discharge space or chamber through the holes 3-1, 3-2 and 33. The metastable atoms impinge upon the side wall of the main discharge chamber to cause secondary electrons to be emitted therefrom, which electrons enter the main discharge space to thereby increase the density of electrons therein, as a result of which a relatively lower voltage may be used as the discharge starting voltage. By utilizing this type of subsidiary discharge, the display device can be simplified in construction.

When the well-known principle of a step discharge tube is employed, the transfer or scanning of the subsidiary discharges can be effected by using a threephase or multi-phase pulse wave. At this point, a conventional display device using the three-phase pulse wave will be described.

FIG. 2 schematically shows in a partially broken perspective view a typical display device adapted to be energized by a three-phase pulse wave and having main discharge anodes 1 and subsidiary discharge anodes 4. It is to be noted that, while only respective ones of the main and subsidiary discharge anodes are shown in FIG. 2, all the other anodes are also arranged in the same manner. In FIG. 2, reference numeral 5 indicates a voltage source for a reset operation, and 6, 7 and 8 represent sources for the scanning pulses. The cathode 2-1 is connected to the voltage source 5, while the pulse sources 6, 7 and 8 are connected to every third one of the other cathodes, respectively.

In more detail, cathodes 2-2, 25, 28, etc. are connected to the voltage source 6, while the cathodes 2-3, 2-6, 2-9 etc. are connected to the voltage source 7. The remaining cathodes 2-4, 27 and 210 etc. are connected to the voltage source 8. The pulse voltages from one and the same pulse source are sequentially applied to every third one of the cathodes to thereby transfer successively the subsidiary discharge in a manner, so to speak, of scanning in three phases. Reference numeral 9 indicates a pulse voltage source to produce signal voltages in accordance with the information to be displayed. This voltage source 9 is connected to the main discharge anode 1-l by way ofa resistor l 1. Furthermore, a direct current source 10 is connected to the subsidiary discharge anode 4-1 through a resistor 12.

FIG. 3 graphically illustrates voltage wave forms of the reset source 5, the pulse sources 6, 7 and 8 for the three-phase scanning, the pulse source 9 and the dc. sources as well as the wave of the subsidiary discharging current (i flowing through the auxiliary anode 4-1, when the brightness modulation of the display device shown in FIG. 2 is performed by the voltage amplitude modulation. The voltage from the pulse source 9 remains zero for-a period 7 after the scanning pulse voltages are applied from the voltage sources 6, 7 and 8. This period is termed the blanking period or duration. During the time interval (T 1 after the blanking period 7 in the duration T of the scanning pulse voltage, a signal voltage is supplied from the pulse source 9 in accordance with the information to be displayed. The purpose of providing the blanking period 1", is to exclude possible erroneous occurrence of the main discharge.

One of the disadvantages of the conventional driving apparatus, as above mentioned, results from the fact that the operation is unstable in the low brightness region. In this low brightness region, the voltage V applied to the main discharge anode 1-1 is at a low level. The time interval t elapsed from the impression of the step-wise voltage V A is increased until the discharge is initiated, as the voltage difference (V -V between the voltage V, and the discharge triggering or starting voltage V decreases. Furthermore, the unevenness of discharge becomes remarkable for each of the spaces formed between the main discharge anodes and the cathodes. This space is hereinafter called a discharge cell or merely a cell.

FIG. 4 shows characteristics of the discharge cells with the ordinate indicating the time t,, while the voltage difference V ,-V is taken along the abscissa. Curve a represents the characteristic of the cell which is the most difficult to discharge, while the curve a is the characteristic of the cell most ready to begin discharge. The dotted broken line extending in parallel to the abscissa indicates the period during which the voltage from the pulse source 9 is continuously applied. In the region above the dotted line, no main discharge can be produced. It is apparent from the graph of FIG. 4 that, in a low brightness region with the voltage V,, being at a low level, some cells produce main discharges, while others are not in the position to discharge, which thus results in the unevenness of the display brightness.

While the above difficulty is applied to the case where the brightness modulation is effected on the basis of the voltage amplitude modulation, a similar problem arises when pulse width modulation or current amplitude modulation is employed. In the case of the pulse width or current amplitude modulation, the voltage amplitude modulation is inevitably mixed due to the presence of a parasitic capacity between the main discharge anode 1-1 and ground. Particularly, this tendency becomes more eminent in the low brightness region. Thus, the problem in the voltage amplitude modulation system as herein-before described will equally be applied to the cases where the pulse width or current amplitude modulation is employed.

Of course, it is conceivable to increase the number of initial electrons in order to reduce the length of t and hence the unevenness in the brightness. In FIG. 4, the broken line indicates the corresponding characteristics in case a sufficient number of initial electrons are available. The curve b indicates the characteristics of the cell most difficult to discharge, while b represents the charactc ristics of the cell most ready to discharge. The difference in the time interval t, between the cells having characteristics b and b is reduced, which effect is attributable to the increase of the initial electrons.

As a means to increase the quantity of the initial or primary electrons, it may be conceived to increase the subsidiary discharge current.

In the prior known display devices, the quantity or number of the initial electrons can be increased by increasing the current isd. However, this method brings about the following drawbacks: (l) at first the amount of light leaking into the main discharge areas through the through-holes 3 is increased, whereby the background becomes brighter to deteriorate the contrast of the display; (2) the dissipation of the electrodes is accelerated by the spattering, resulting in the shortening of the life of display elements; and (3) the device becomes more susceptible to erroneous operations.

FIG. shows the relationship between the subsidiary discharge current (isd) and the minimum period (T min of the scanning pulse, which does not give rise to the erroneous operation. It can be seen from FIG. 5 that (T min becomes a minimum at a certain value of (isd) and increases at the other values of the latter. Accordingly, if the current (isd) is to be increased, the scanning rate must be decreased. Otherwise, erroneous operation may not be evaded. For this reason, the use of increased current (isd) is not a preferable measure.

SUMMARY OF THE INVENTION An object of the present invention is to provide a display device of a high quality to display characters, numerals, figures, patterns or the like wherein the disadvantages and drawbacks of the conventional devices are substantially eliminated.

To this end, according to the invention, a pulse voltage source is used in place of the direct current source and the resistor 12 of the conventional display device shown in FIG. 2. By appropriately setting the magnitude and the time duration of pulse voltage or current from the source to predetermined values, the dc. component of the subsidiary discharge current can be made smaller. The delay time t, as well as the inequality thereof are considerably reduced. Thus, according to the present invention, an improved display device which gets rid of the disadvantages of the conventional devices and can display a stabilized image with better contrast has been provided. The apparatus of the invention has, of course, a longer usable life than the prior ones. I

The other objects, advantages and novel features 0 the present invention will be made apparent from the detailed description of a preferable embodiment of the invention. The description makes reference to the drawings.

BRIEF DESCRIPTION OF THE INVENTION FIG. 1 is a partial perspective view of an electrode arrangement of a known display device used for better understanding of the present invention;

FIG. 2 schematically shows a structure of the conventionaldisplay device in a partial perspective view;

FIG. 3 graphically shows wave forms of voltages and currents applied to various electrodes of the apparatus shown in FIG. 2;

FIG. 4 is a graph illustrating the relation between the applied voltage and the delay time of the discharge occurrence;

FIG. 5 is a graph showing the relation between the subsidiary discharge and the minimum scanning pulse period;

FIG. 6 is a perspective view showing schematically and partially a structure of a display device according to the present invention;

FIG. 7 illustrates a typical voltage wave applied to an anode for the subsidiary discharge in the device according to the invention;

FIG. 8 is a graph to illustrate the relation between the main discharge voltage and the brightness of a display device manufactured according to the invention;

FIGS. 9 and 10 graphically show brightness characteristics of the devices embodying the invention;

FIG. 1 1 illustrates another example of a voltage wave as applied to an anode for the subsidiary discharge; and

FIGS. 12a, 12b and 120 and FIG. 13 are schematic circuit diagrams of pulse sources which can be employed in the embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 6 which shows a main portion of an embodiment of the inventive display device, the difference from the arrangement shown in FIG. 2 resides in that a pulse voltage source 10' is employed in place of the dc. source 10 and the resistor 12 of FIG. 2. It is to be noted that the same numerals in FIG. 6 indicate the same or equivalent elements to those shown in FIG. 2.

FIG. 7 shows graphically the wave forms of pulse voltage Vsd (two pulses are used in the illustrated example) applied to the anode for the subsidiary discharge from the pulse source 10' by way of a resistor (internal resistor contained in the source 10'), subsidiary discharge current (isd), and the scanning or transfer pulses from the source 6. Although the wave forms of the voltages from the reset source 5, and the voltage sources 7 and 8 are not shown, it should be appreciated that they are the same as those shown in FIG. 3.

Pulse I of the pulse voltage Vsd is used to produce initial electrons in the main discharge region, while pulse II serves to facilitate the transfer of the discharge in the subsidiary discharge area. In other words, the pulse I can be applied to the subsidiary discharge anode 4-1 as a pulse having a relatively greater amplitude (for example, a. 2mA) for a predetermined duration as described hereinafter, so that the application of the pulse from the signal source 9 can bring about the main discharge without fail. Thus, the pulse I plays a main role in rein accordance with objects to be displayed, images of 5 very high quality can be displayed.

By way of an example, FIG. 8 shows a result of the measurements of 2,000 discharge cells with respect to the relation between the brightness (fL) and the voltage (V) applied across the main discharge anode l and the cathode 2 with T of 6411s, 18,; of l9,u.s, rd. of l9us, 'rd of 62,us, rw and 7W2 both of 2p.s and the peak value i of (isd) set to 2 mA. The unevenness of brightness among cells is neglected. The applied voltage is expressed in terms of the excess voltage beyond the main discharge starting voltage. Solid curves 0 and 0' show the characteristics of the display device according to the invention. The curve c represents the cell most ready to discharge while the curve c is for the cell most difficult to discharge. The dotted lines a and a are the characteristic curves of conventional display devices with the curve 0 for the most easily dischargeable cell and the curve 0 for the cell most difficult to discharge. The maximum brightness of the display device was 13 fL.

According to the present invention, the subsidiary discharge current on an average can be made smaller and thus the background brightness due to the leakage of light caused by the subsidiary discharge can be decreased to 0.2 fL which is lower than a half of the background brightness of the conventional device, which was 0.5 fL. The contrast attained in the display device according to the present invention is therefore 65 l as expressed in terms of the ratio between the maximum and the minimum brightnesses. On the other hand, the corresponding contrast in the case of the conventional device was 26 l. The brightness at the lowest level which can be discriminated from the background was 0.4 fL at the excess voltage of 20 V. On the contrary, in case of the conventional display device, the corresponding brightness level was 1.3 fL at the excess voltage of 37 V. In the voltage range lower than 37 V, a discharge did not take place in some cells. Accordingly, the number of gray scales determined by dividing linearly the brightness between the maximum and the minimum levels is 13 (fL)/0.4(fL) 32. In the conventional device, the number of gray scales was only l3(fL)/l.3(fL) 10. As is apparent, the ratio of contrast as well as the number of gray scales can be considerably improved.

Next, FIGS. 9 and show results of the measurements concerning the pulse widths and phases of the pulses applied to the subsidiary discharge anodes 4. In more detail, FIG. 9 shows the relation between the pulse widths of the pulses I in FIG. 7 and the brightness. The background brightnesses at the excess voltage OV applied to the main discharge electrode are indicated by a symbol and the background brightnesses at the excess voltage of 25 V are represented by A. In the absence of the pulse I (namely, w O), the main discharge is not initiated and the brightness is equal to the level at the excess voltage of CV (background brightness level). However, when the pulse having a pulse width greater than 1 us is impressed, a normal discharge will occur and the production of the normal gray scale is now possible.

FIG. 10 shows the relation between the brightness and rd of the discharge cell having the lowest brightness in the measurements shown in FIG. 9. The value of *rw was 2 ,us. It was found that the brightness was at a maximum when rd was selected to be substantially equal to the blanking period rB The range of rd, in

which a relatively higher brightness was attained was TB" 3 MS.

In the experiment on the pulses to transfer the subsidiary discharge, it was seen that the most stable scanning was obtained by the pulse 11 which is positioned at the termination of the scanning period T No erroneous operation was caused by the pulse II which occurs in the range of i 10 p.s from said termination.

In the foregoing, description has been made with reference to the case where two pulses are applied to the subsidiary discharge anode. However, it was further found that the same effect could be obtained by using a single pulse superposed on a d.c. voltage. FIG. 11 shows the voltage wave form in this case. The most suitable values of *rd and TW, were the same as those obtained in the measurements shown in FIGS. 9 and 10.

Additionally, it is assumed in the above description that the pulses I and II comprise, respectively, a single pulse. However, the same results could be obtained when the pulses I and/or II each composed of a plurality of pulses are employed.

FIGS. 12a, 12b and show examples of the arrangements of the above-described pulse source 10. The circuit of FIG. 12a is composed of a pulse generator 13 and a resistor 14. The circuit of FIG. 12b comprises a pulse source 13, a transistor 18, a resistor 19 and a dc. source 20 connected to vary the current pulsewise. In the circuit of FIG. 12, a combination of the pulse source 13 and the dc. source 17 is employed together with resistors 14 and 16 and a diode 15 to superpose pulses on a small current. It should, however, be understood that the pulse source 10' employed in accordance with the present invention is not to be re stricted to these circuits. Any circuit arrangement which is capable of varying the voltage or current pulsewise may be used. In this connection, it is not preferable to provide pulse sources for each of the subsidiary discharge anodes of the display device, because the circuit connection is thereby much more complicated. For this reason, a circuit arrangement such as shown in FIG. 13 may be employed, when a number of the subsidiary discharge anodes are to be driven by the source circuit of the fundamental construction shown in FIG. 12c. Namely, each of the subsidiary discharge anodes is connected to a common pulse source 13 by way of a resistor and a diode 15.

The invention has been described in the above in connection with the case wherein the electrode common to both of the main and the subsidiary discharges is used as the cathode with the other electrode being used as the anode. However, the present invention is equally applicable to the case where the polarities of the electrodes are reversed.

According to the presentinvention, the contrast of the image can be remarkably improved and the unevenness in the low brightness region can be greatly reduced. Thus, an image display device of high performance has been accomplished.

Although the invention has been described with reference to a preferred embodiment, it should be appreciated that many modifications and changes may be made in the form of the invention without departing from the spirit and scope of the invention.

We claim:

1. A display device providing discharges in a gas, comprising a plurality of first electrodes for main discharges, a plurality of second electrodes for subsidiary discharges, a plurality of third electrodes disposed so as to intersect said first and second electrodes to produce said main and subsidiary discharges at the points of intersection in cooperation with said first and second electrodes, a gas-filled enclosure containing said first, second and third electrodes, a first electric energy source to supply a pulse wave to said third electrodes with a predetermined period to thereby transfer said discharges between third electrodes, a second electric energy source connected to supply a pulse wave having a predetermined period to said second electrodes to thereby produce said subsidiary discharge, and a third source connected to apply a signal to be displayed to said first electrodes to thereby produce said main discharges simultaneously with said subsidiary discharges.

2. A display device as set forth in claim 1, characterized in that said second source supplies said pulse wave superposed on a direct current.

3. A display device as set forth in claim 1, wherein said first and second electrodes are elongated conductive members disposed in spaced parallel relationship in respective superposed sets and said third electrodes that said third electrodes operate as cathodes, and said second and third signal sources provide voltages having a polarity such that said first and second electrodes operate as anodes.

5. A display device as set forth in claim 4, wherein said second source comprises a pulse source connected through a resistor to each second electrode.

' 6. A display device as set forth in claim 4, wherein said second source comprises a transistor having an input electrode connected to a pulse voltage source, a first output electrode connected through a resistor to a dc source, and a second output electrode connected to each second electrode.

7. A display device as set forth in claim 4, wherein said second source comprises a pulse circuit including a first resistor, a diode and a pulse voltage source connected in series, and a dc. circuit including a second resistor and a dc. source connected in series, said pulse circuit and said do. circuit being connected in parallel to each second electrode. 

1. A display device providing discharges in a gas, comprising a plurality of first electrodes for main discharges, a plurality of second electrodes for subsidiary discharges, a plurality of third electrodes disposed so as to intersect said first and second electrodes to produce said main and subsidiary discharges at the points of intersection in cooperation with said first and second electrodes, a gas-filled enclosure containing said first, second and third electrodes, a first electric energy source to supply a pulse wave to said third electrodes with a predetermined period to thereby transfer said discharges between third electrodes, a second electric energy source connected to supply a pulse wave having a predetermined period to said second electrodes to thereby produce said subsidiary discharge, and a third source connected to apply a signal to be displayed to said first electrodes to thereby produce said main discharges simultaneously with said subsidiary discharges.
 2. A display device as set forth in claim 1, characterized in that said second source supplies said pulse wave superposed on a direct current.
 3. A display device as set forth in claim 1, wherein said first and second electrodes are elongated conductive members disposed in spaced parallel relationship iN respective superposed sets and said third electrodes are elongated flat strips disposed transverse to and between said superposed sets of first and second electrodes and having holes therein located at the points of intersection of said electrodes.
 4. A display device as set forth in claim 3, wherein said first signal source provides a voltage polarity such that said third electrodes operate as cathodes, and said second and third signal sources provide voltages having a polarity such that said first and second electrodes operate as anodes.
 5. A display device as set forth in claim 4, wherein said second source comprises a pulse source connected through a resistor to each second electrode.
 6. A display device as set forth in claim 4, wherein said second source comprises a transistor having an input electrode connected to a pulse voltage source, a first output electrode connected through a resistor to a d.c. source, and a second output electrode connected to each second electrode.
 7. A display device as set forth in claim 4, wherein said second source comprises a pulse circuit including a first resistor, a diode and a pulse voltage source connected in series, and a d.c. circuit including a second resistor and a d.c. source connected in series, said pulse circuit and said d.c. circuit being connected in parallel to each second electrode. 